A peritoneal dialysis solution generally contains three functional constituents. First, it contains electrolytes, which in this case are calcium. sodium and magnesium salts which, as a rule, are used in chloride form. A buffer is provided as the second functional constituent. The best tolerated buffer system consists of bicarbonate that is at equilibrium with carbonate in the alkaline region and with CO.sub.2, in the acid region. Substances that buffer at a pH of approximately 7, that is, at a physiological pH, could also be used as buffers. Substances which can easily be metabolized to bicarbonate inside the body. such as lactates, pyrovates or similar substances, are preferred. The third functional constituent consists of an osmotic substance. Here, glucose is frequently used, which at a relatively low concentration has a high osmolarity and is well tolerated. One reason for the frequent use of glucose is its favorable price compared to other substances that might be used as the osmotic substance.
WO 96/01118 discloses, for example, a solution for peritoneal dialysis or infusion, bicarbonate is used in physiological quantities of 20-30 mEq/l together with a weak acid in a quantity of 10-20 mEq/l. When such a peritoneal dialysis solution is used. it is necessary that the bicarbonate contained and the calcium contained be stored separately, as storing them together very easily leads to an insoluble calcium carbonate precipitation. In the acid region, this, precipitation can be avoided, as the bicarbonate continues to be at equilibrium with the carbon acid, and so with CO.sub.2, so that less carbonate is present. However, this has the disadvantage that a relatively high CO.sub.2 partial pressure is created. This high CO.sub.2 partial pressure in turn requires a bag film with an effective CO.sub.2 banier so that especially adapted bags with a relevant CO.sub.2 barrier layer can be used.
In EP 0 076 355 A the bicarbonate has, for example, been replaced by lactate as the buffer to avoid problems in the handling of a solution containing bicarbonate. However, the use of lactate causes another problem during heat sterilization, as lactate and the glucose that is also present in the solution react to form acetaldehyde. Acetaldehyde, however, damages the peritoneal walls.
Furthermore, heat sterilization also causes glucose to be caramelized, isomerized or broken down into products which can continue to react irreversibly with proteins inside the body. This and other problems led in EP 0 076 355 A to the replacement of glucose, for example, by glucose polymers (such as icodextrine), peptides or proteins such as albumin. This glucose replacement, however. leads to a considerable price increase of the product. In addition, physiological reactions, such as immune reactions, were observed with the use of these substitutes. Finally, similar problems to those of glucose could also be observed with glucose polymers during heat sterilization so that different ways had to be found to avoid the glucose breakdown.
In this respect WO 93/09820 teaches on the one hand separate storage for a corresponding system and, on the other hand, short but high-temperature heating for the purpose of sterilization. In the case of separate storage. glucose is largely stored in a separate container to avoid reactions with other constituents such as lactate. According to this teaching, the glucose solution can be heated briefly and at very high temperature while the solution together with the other constituents can be subjected to the usual sterilization conditions without problems.
Another way of solving the problems described with regard to EP 0 076 355 A is described in WO 91/08008 where sterilization can be performed at very low pH values of below 3. This again leads to the problem that at these low pl I values a weak acid, such as lactic acid or its salt. the lactate, is not sufficient as a weak base for buffering to achieve a physiological pH of around 7.2 to 7.4 in a final solution.